The main functions of the Dosimetry Core are to acquire accurate radiation dosimetry data for the MM-50 microtron, and to assure proper delivery of the dose to the patient. These include (1) dosimetry calibration, (2) beam data acquisition and conversion of raw data into tables for treatment planning use, (3) establishment of machine performance standards and procedures for quality assurance, (4) implementation of real-time imaging devices, and (5) implementation of in-vivo dose monitoring system. Radiation dosimetry determines the absorbed dose delivered to the patient which is important to the study of dose escalation in the clinical studies (Research Project I). Basic beam data are needed by the treatment planning programs used in plan design, evaluation and optimization (Research Project II). In addition, beam data are used in the development of the algorithm for multi-leaf collimator dosimetry (Research Project III). Machine performance standards are defined in accordance with the specifications established jointly by MSKCC and by Scanditronix, the manufacturer of the MM-50. Regular quality assurance ensures that the machine is in a proper and safe working condition to provide reliable and smooth delivery of treatments. Real time imaging is an important tool for treatment verification and uncertainty analysis (Research Project III). In-vivo dose monitoring provides an additional assurance that accurate dose is delivered. Some of the work in the Dosimetry Core are in collaboration with the Clinical Core and the Computer Core. A variety of equipment is available for radiation dosimetry tasks, including: a three dimensional dose measurement system, an assortment of ionization chambers, a thermoluminescent dosimetry (TLD) system, a film densitometer, an anthropomorphic phantom, and an on-line imaging system. In addition, a VAX computer cluster system, consisting of a VAX-8550, a VAX-8810, and two VAXstations, is available for beam data acquisition, data analysis, and other related work.